4 SMALL WATER SUPPLIES. 



jurious and demand expensive treatment in their 

 extermination. As stated, the nitrogenous com- 

 pounds are the most dangerous and the determina- 

 tion of their quantity is of paramount importance. 

 They are generally present in the form of ammonia, 

 albuminoid ammonia, nitrates and nitrites. The 

 second named is the most dangerous. It bespeaks 

 certain nitrogenous matter in an undecomposed 

 state in solution, and must not be present in any 

 supply in quantities over one in ten million. 



Again, all waters will contain that constituent of 

 common salt known as Chlorine. It may be regarded 

 as the result of animal pollution. The estimation of 

 what constitutes an abnormal quantity of chlorine 

 is, however, a difficult matter. Again, organic im- 

 purities, although not perhaps likely to be directly 

 dangerous to health, may be conducive to the de- 

 velopment of organized growths with water. Again, 

 a bacterial examination of a supply is often useful, 

 especially if it is in any way suspected of being 

 harmful. By this method the number and varieties 

 of well-known microbes contained in the water are 

 revealed. Again, we have what are known to the 

 public as hard and soft waters. Spring water, well 

 water, and water from streams flowing in limestone 

 districts are liable to be hard. That is to say, 

 although usually free from suspended matter, they 

 contain dissolved mineral matter in considerable 

 quantities, consisting usually of carbonates of lime, 

 magnesia, calcium, manganese and iron. These are 

 held in solution by an excess of CO 2 . In a lesser 

 degree we have calcium sulphates, and chloride 

 and magnesium sulphate or chloride. The presence 



